1. Field of the Invention
The present invention relates to a telescopic boom including three or more sections which may be pivoted if desired, and of which the innermost section is constituted by a housing which is incapable of moving in the longitudinal direction, whereas the other sections are adapted to be concurrently dislocated in the longitudinal direction relative to the respective adjacent sections located inwardly thereof, when the boom is to be lengthened or shortened.
2. Description of the Prior Art
In known telescopic booms hydraulic cylinders are mostly used for the extension and retraction of the boom. For each telescope section there may then be used a cylinder housed in its own telescope section, or a cylinder common to all of the telescope sections may be used.
Due to the different effective cylinder area during extension or retraction of the cylinder section, respectively, such known telescopic booms suffer from the disadvantage that the pushing force and the pulling force are not equal. Besides, when using hydraulic cylinders, sealing problems will occur due to wear of the guiding portions.